Signalling method

ABSTRACT

The invention relates to methods for transmission of signalling data in cellular telecommunication networks. According to the invention, multiple radio bearers can be allocated for transferring signalling traffic, but all higher layer signalling is in any case taken through the RRC protocol. In the inventive method, MM and higher layer messages are sent using RRC DIRECT TRANSFER messages, but a separate RLC entity is set up for RRC DIRECT TRANSFER messages. In various embodiments of the invention, separate radio bearers can be set up for individual CN domains and/or upper layer protocols and/or for a group of RRC messages.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to methods for transmission of signalling data incellular telecommunication networks. Especially, the invention isrelated to such a method as specified in the preamble of the independentmethod claim.

2. Description of Related Art

The current concept of a signalling radio bearer in the UMTS system(universal mobile telecommunication system) defines that there is onlyone radio bearer for signalling traffic between the cellular network anda mobile communication means. Both the RRC (radio resource control) andhigher protocol layers use the same radio bearer, i.e. the same RLC(radio link control) entity. In some implementations it is possible tohave two RLC entities for signalling traffic, one entity forunacknowledged mode transfer and one entity for acknowledged modetransfer. However, there is currently no means to treat these entitiesseparately for example for setup, reconfiguration or release. Thesignalling radio bearer, sometimes called the signalling link, is set upduring the RRC connection establishment procedure. In someimplementations, it is even possible that the radio bearer service isactually provided by the PDCP layer. In this case the PDCP will run intransparent mode for signalling traffic.

Higher layer messages, such as MM (mobility management) or CM(connection management) layer messages are carried between a mobilecommunication means and the network in a RRC DIRECT TRANSFER messagepayload. The protocol stack is illustrated in FIG. 1. FIG. 1 shows anexample of a partial protocol stack of a circuit switched core network(CN) domain, which protocol stack comprises connection management (CM)and mobility management (MM) protocol layers, and an example of aprotocol stack of a packet switched core network domain, which protocolstack comprises session management (SM) and packet switched domainmobility management (PMM) protocol layers. Both of these protocol stackscommunicate with the RRC (radio resource control) layer, which handlesthe transmission of the higher layer protocol messages in a RRC DIRECTTRANSFER MESSAGE payload. The radio link control protocol can be set upto provide unacknowledged or acknowledged data transmission service.Each RLC instance is configured by RRC to operate in one of three modes:transparent mode (Tr), unacknowledged mode (UM) and acknowledged mode(AM). The transparent and unacknowledged mode are used by some of theRRC signalling procedures. Majority of RRC signalling proceduresincluding the Direct Transfer procedure utilize acknowledged modetransfer. The service that the RLC layer provides to upper layers iscalled radio bearer (RB). A radio bearer with the corresponding Iubearer comprises a radio access bearer (RAB).

The problems with the prior art solution used at the time of writingthis patent application are mainly related to priority control ofsignalling traffic. A problem can arise for example in a case, when avery long higher layer message is passed to RLC layer which buffers themessage, and when a time critical RRC message also needs to be sent. Inthis situation, the RLC layer transmits the buffered messages firstbefore transmitting more recent messages, which results in a delay ofthe time critical RRC message. Currently there are no mechanismsallowing priorization of more recent messages over those messageswaiting in RLC transmission buffer. It is also possible that higherlayer signalling such as MM and CM will need some prioritization meansbetween the various higher layer protocols.

At the time of writing this patent application, a requirement hasrecently been identified which may finally require that severalsignalling radio bearers can be set up so that different QoS (quality ofservice) parameters can be used for different types of signalling. Onesolution for this requirement has been proposed. According to thissolution, MM and higher layer signalling is carried over the airinterface like any user traffic, in a separate radio bearer. Thissolution creates some problems related to integrity controlfunction—which is defined as a RRC layer function—and to the existingprocedures in Iu interface.

FIG. 2 illustrates protocol stack configuration for signalling transferaccording to a recently proposed solution. According to this solution,signalling traffic of MM and other higher layer protocols aretransmitted directly using PDCP services. In this solution, onlyfunction that would be required from PDCP layer is the integrityprotection. According to the solution, either one user plane radiobearer is used for all higher layer signalling protocols or a separateuser plane radio bearer is allocated for each higher layer protocolstack. In the example of FIG. 2 each CN domain employs a different radioaccess bearer (RAB) for signalling between UE and each CN domain.According to this solution, priority control between MM and RRC messagescan be handled in RLC/MAC using normal radio bearer/logical channelpriority control mechanisms.

This proposal has some disadvantages. For example, the proposed solutionincreases the complexity of the MM and PMM protocol implementations,since primitive interfaces arc needed not only for the RRC protocol, butfor the PDCP protocol as well. The proposed solution would also be anaddition to current PDCP functions and change radically the basicfunction of PDCP as a packet service dependent sublayer. This would addcomplexity to the implementations of the PDCP protocol. Further, sincePDCP is only intended for transmission of user plane traffic, in theproposed solution UE-CN signalling would be treated like user planetraffic, which implies that some modifications will most probably beneeded also to the current Iu interface specifications. Further, in theproposed solution integrity protection needs to be implemented in twoplaces: in PDCP layer for MM and higher layer signalling and in RRClayer for RRC signalling. As a consequence, the complexity of PDCPprotocol increases and an additional header field is needed in PDCP datapayload data units (PDU), since the integrity function requires acounter value to be transmitted with each piece of integrity protecteddata for use by the integrity protection algorithm.

SUMMARY OF THE INVENTION

An object of the invention is to realize a signalling method, whichalleviates the aforementioned problems of prior art. A further object ofthe invention is to provide a method for transmission of controlsignalling, which allows determining of quality of service levels fordifferent signalling traffic streams.

A still further object of the invention is to provide the aforementionedobjects of the invention, without adding complexity in the protocollayers above the RRC protocol layer.

The objects are reached by setting up at least two signalling radiobearers for transmission of signalling traffic, and specifying rules forrouting of higher layer signalling to the signalling radio bearers.

The method according to the invention is characterized by that, which isspecified in the characterizing part of the independent method claim.The network clement according to the invention is characterized by that,which is specified in the characterizing part of the independent claimdirected to a network element. The mobile communication means accordingto the invention is characterized by that, which is specified in thecharacterizing part of the independent claim directed to a mobilecommunication means. The dependent claims describe further advantageousembodiments of the invention.

According to the invention, at least two signalling radio bearers areset up for transmission of signalling traffic and the cellular networkconfigures how the signalling of higher layer protocols is mapped tosaid signalling radio bearers. Multiple radio bearers can be allocatedfor transferring signalling traffic, but all higher layer signalling isin any case taken through the RRC protocol.

In the inventive method, MM and higher layer messages are sent using RRCDIRECT TRANSFER messages, but separate RLC entities can be set up forRRC DIRECT TRANSFER messages. In various embodiments of the invention,separate radio bearers can be set up for individual CN domains and/orupper layer protocols and/or for a group of RRC messages.

Routing of messages to signalling bearers can advantageously beperformed on the basis of CN domain identity information contained inevery RRC DIRECT TRANSFER data unit. In embodiments, in which separateradio bearers are set up for different upper layer protocols ordifferent groups of upper layer protocols, the routing of RRC DIRECTTRANSFER data units is advantageously performed on the basis ofexamination of the contents of data units and interpreting, with whichprotocol each data unit is associated.

The inventive method provides integrity protection of MM and higherlayer messages as a consequence of the transmission of the messages inRRC DIRECT TRANSFER messages. The inventive method allows controlling ofpriority between MM and higher layer messages and RRC messages in theradio interface by adjusting the QoS parameters of bearers used totransfer the messages.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail in the following withreference to the accompanying drawings, of which

FIG. 1 illustrates protocol stack configuration for signalling transferaccording to prior art,

FIG. 2 illustrates protocol stack configuration for signalling transferaccording to another solution of prior art,

FIG. 3 illustrates protocol stack configuration for signalling transferaccording to an advantageous embodiment of the invention,

FIG. 4 illustrates RRC signalling related to radio bearers,

FIG. 5 illustrates a method according to an advantageous embodiment ofthe invention,

FIG. 6 illustrates an example of the structure of a radio networkcontroller according to an advantageous embodiment of the invention, and

FIG. 7 illustrates an example of the structure of a mobile communicationmeans according to an advantageous embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A. A First Group of Advantageous Embodiments of the Invention

FIG. 3 illustrates protocol stack configuration for signalling transferaccording to an advantageous embodiment of the invention. This figureillustrates the example case that a separate radio bearer is reservedfor each CN domain. In FIG. 3, each radio bearer is represented by a RLCentity corresponding to the radio bearer. FIG. 3 illustrates, thatsignalling from the circuit switched CN domain (CM, MM) is transmittedvia a second RLC entity 102, while signalling from the packet switchedCN domain (SM, PMM) is transmitted via a third RLC entity 103, while afirst RLC entity is used for transmission of the rest of RRC messages.

According to the invention, the RRC protocol can use one or moresignalling radio bearers (SRB) i.e. RLC entities for transmission ofsignalling traffic between the network and the mobile communicationmeans, i.e. UE (user equipment). In other words, the signalling linkbetween a UE and a RNC (radio network controller) can comprise one ormore signalling radio bearers.

The UE can be commanded to use only one signalling radio bearer for allsignalling. An additional signalling radio bearer can be set up and theRRC layer and the UE can be configured to send all RRC DIRECT TRANSFERmessages using this additional signalling radio bearer. Further, morethan one signalling radio bearers can be set up by the network.Preferably, the network makes the decisions about the configuration ofthe signalling radio bearers.

Different rules for using the more than one signalling radio bearers canbe used in different embodiments of the invention.

For example, in an advantageous embodiment of the invention, separatesignalling radio bearers are used for each CN domain protocol stack.Such an embodiment is illustrated in FIG. 3. In such an embodiment, theRRC layer can route the RRC DIRECT TRANSFER messages to correct radiobearer by checking the CN domain identification information in the dataunits comprising the messages.

As a second example, in an advantageous embodiment of the invention,separate signalling radio bearers are used for each higher layerprotocol. In such an embodiment, the RRC layer can route the RRC DIRECTTRANSFER messages to correct radio bearer by checking the NAS (networkaccess stratum) protocol discriminator information in the data unitscomprising the messages.

As a third example, in an advantageous embodiment of the invention,separate signalling radio bearers are used for various predefined groupsof higher layer protocols. In such an embodiment, the RRC layer canroute the RRC DIRECT TRANSFER messages to correct radio bearer bychecking the NAS (network access stratum) protocol discriminatorinformation in the data units comprising the messages. In such anembodiment, each signalling radio bearer carrying higher level protocolsignalling has a corresponding pre-defined set of NAS protocoldiscriminators.

The invention is not limited to these rules for deciding about the usageof the signalling radio bearers, since other types of rules can as wellbe used. For example, the decision of which signalling radio bearer touse for any given message can in an embodiment of the invention based onthe PDU size. In such an embodiment, the length of each message ischecked, and the bearer to be used is selected at least partly on thebasis of the result of this checking.

In a further advantageous embodiment of the invention, the routing isbased on a Quality of Service parameter attached to the higher layerprotocol data. In such an embodiment, higher layer protocols may add aQoS parameter to single messages, to plurality of messages, or forexample to all messages in order to ensure, that the messages are routedvia a signalling radio bearer fulfilling the desired QoS level. In suchan embodiment, the RRC layer can route the RRC DIRECT TRANSFER messagesto correct signalling radio bearer by checking the additional QoS classinformation from the data units comprising the messages. There can befor example a predefined set of QoS classes for higher layer signallingmessages, for example two QoS classes, or the number of QoS classes canbe decided by the network. Preferably, for each QoS class a separateradio bearer is set up. An example of this QoS class separation could bethe short message service (SMS) which could use lower priority thanother signalling.

The functionality for performing the decisions about the number ofsignalling radio bearers and about the rules for dividing traffic tothese signalling radio bearers can be implemented in many differentnetwork elements of a radio access network (RAN). Preferably, thenetwork element performing the decisions about the number of signallingradio bearers and about the rules for dividing traffic to thesesignalling radio bearers is the radio network controller (RNC).

In a further embodiment of the invention, the rules to be used can beselected out of a predefined set of rules by using the number ofsignalling radio bearers. In this embodiment, each possible amount ofsignalling radio bearers is associated with a predefined set of rules.

In a further advantageous embodiment of the invention, one of thesignalling radio bearers can be defined as a master signalling radiobearer. This radio bearer is set up only in the RRC connectionestablishment procedure and released only in the RRC connection releaseprocedure. This master SRB would be used as the prior art signallingbearer. Such an embodiment ensures, that all signalling bearers are notreleased in error during the RRC connection, since the master SRB inthis embodiment cannot be controlled by radio bearer control messages.

B. A Second Group of Advantageous Embodiments of the Invention

In an advantageous embodiment of the invention, the messages used forcontrolling radio bearers are used for controlling the signalling radiobearers as well. The messages are the RRC CONNECTION SETUP, RADIO BEARERRECONFIGURATION, RADIO BEARER RELEASE, and RADIO BEARER SETUP messages.The usage of the messages is described in the following with referenceto FIG. 4. In the prior art, these messages are only used to control theuser-plane radio bearers, not signalling. More details of the prior artuse of these messages and a description of the other messages of the RRCprotocols can be found in the RRC protocol specifications of the UMTSsystem. FIG. 4 illustrates four RRC layer procedures, namely RRCconnection establishment, radio bearer setup, radio bearerreconfiguration, and radio bearer release procedures. The RRC connectionestablishment procedure initiates the RRC connection between the mobilecommunication means and the network, while the other three of these fourprocedures listed here are used to control single radio bearers and mayor may not occur during the lifetime of a RRC connection. FIG. 4 showssignalling between a mobile communication means (UE, user equipment) andthe radio access network (UTRAN, UMTS terrestrial radio access network).

The RRC connection establishment procedure is initiated by the UE, whichsends 300 a RRC CONNECTION REQUEST message to the radio access network.The radio access network responds to the message by sending a RRCCONNECTION SETUP message, which comprises information about variousparameters about the RRC connection to be established. The UE finishesthe RRC connection establishment procedure by sending 310 a RRCCONNECTION SETUP COMPLETE message.

The radio bearer setup procedure is initiated by the network, whichsends 320 a RADIO BEARER SETUP message to the UE. The message comprisesinformation about various parameters of the radio bearer about to beestablished. The UE responds to the message by sending 325 a RADIOBEARER SETUP COMPLETE message.

The radio bearer reconfiguration procedure is initiated by the network,which sends 330 a RADIO BEARER RECONFIGURATION message to the UE. Themessage comprises information about new values of parameters for theradio bearer or bearers affected. The UE responds to the message bysending 335 a RADIO BEARER RECONFIGURATION COMPLETE message.

The radio bearer release procedure is initiated by the network, whichsends 340 a RADIO BEARER RELEASE message to the UE. The messagecomprises information identifying the bearer to be released. The UEresponds to the message by sending 335 a RADIO BEARER RELEASE COMPLETEmessage.

According to an advantageous embodiment of the invention, the setting upand configuration of all the signalling radio bearers is done during theRRC connection establishment procedure. This can advantageously beeffected by adding information about the signalling radio bearers to beestablished to the RRC CONNECTION SETUP message. One advantageousexample of the organization of such information is presented later inthis application.

In one advantageous embodiment of the invention, only one signallingradio bearer is set up and configured during the RRC connectionestablishment procedure. In such an embodiment, further signalling radiobearers can be set up and configured later during the RRC connection, ifneed for that arises.

In an advantageous embodiment of the invention, the radio access networkcan set up additional Signalling Radio Bearers during the RRC connectionand configure how the higher layer signalling is mapped into the new andexisting signalling radio bearers. This can advantageously be effectedby adding information about the signalling bearers to be established tothe RADIO BEARER SETUP message. One advantageous example of theorganization of such information is presented later in this application.

In an advantageous embodiment of the invention, the radio access networkcan re-configure the mapping between higher layer signalling and anyexisting signalling radio bearer during the RRC connection. This canadvantageously be effected by adding information about the signallingbearers to be reconfigured to the RADIO BEARER RECONFIGURATION message.One advantageous example of the organization of such information ispresented later in this application.

In an advantageous embodiment of the invention, the radio access networkcan release any signalling radio bBearers during the RRC connection andreconfigure the mapping between higher layer signalling and anyremaining signalling radio bearers. This can advantageously be effectedby adding information about the signalling bearers to be released andthe new reconfiguration information to the RADIO BEARER RELEASE message.One advantageous example of the organization of such information ispresented later in this application. The following paragraphs and tablesshow examples according to various advantageous embodiments of theinvention about how information pertaining to signalling radio bearerscan be presented in the referred messages.

In the RRC CONNECTION SETUP message, the information about signallingradio bearers can be presented among the radio bearer informationelements as shown in the following table. Note that for clarity, thefollowing table lists only radio bearer (RB) information elements of themessage.

RB information elements Information Element Range Signalling RadioBearer 0 to <MaxSRBCount> information RB identity Signalling RadioBearer type RB mapping info SRB mapping info

The parameter “Signalling Radio Bearer information” indicates the numberof signalling radio bearers. The other four parameters are then repeatedthe indicated number of times. The parameter “RB identity” identifiesthe radio bearer. The purpose of the “Signalling Radio Bearer Type”information element is to indicate the RLC parameters needed for theSignalling Radio Bearer. Advantageously, each possible value of“Signalling Radio Bearer Type” information element refers to apredefined set of parameters. The parameter “RB mapping info” indicates,as in prior art, details about multiplexing RLC frames to physical layerchannels. The parameter “SRB mapping info” indicates how variousprotocol messages are mapped to the particular SRB. The parameter“MaxSRBCount” defines the maximum number of signalling radio bearers.

In the RADIO BEARER RECONFIGURATION message, the SRB information can berepresented by a “SRB mapping info” parameter among the RB informationelements. The parameter is optional, and only present if the particularradio bearer is a signalling radio bearer.

In the RADIO BEARER RELEASE message, the SRB information can berepresented by a “SRB mapping info” parameter among the RB informationelements. The parameter is optional, and only present if the particularradio bearer is a signalling radio bearer.

In the RADIO BEARER SETUP message, the SRB information can berepresented by a “SRB mapping info” parameter among the new RBinformation elements, if the particular new RB is to be a SRB, and by a“SRB mapping info” parameter among information elements for other radiobearers affected by the message, if the particular other RB is a SRB.These parameters are optional, and only present if the particular radiobearer is a signalling radio bearer.

In one advantageous embodiment of the invention, the allowed values of“SRB mapping info” parameter i.e. information element range from 0 to 7with the following meanings:

-   -   0 all RRC signalling    -   1 all RRC signalling except RRC Direct Transfer messages    -   2 all RRC Direct Transfer messages    -   3 RRC Direct Transfer messages with specified CN Domain        Identities    -   4 RRC Direct Transfer messages carrying NAS message with the        specified PD    -   5 only the specified RRC messages    -   6-7 reserved for future use

If the value is 3, 4, or 5, then also information elements describingdetails of correspondingly CN domain identities, NAS PD information, andRRC message types are present.

C. A Third Group of Advantageous Embodiments of the Invention

FIG. 5 illustrates a method according to an advantageous embodiment ofthe invention. FIG. 5 illustrates a method for transmission ofsignalling data in a cellular telecommunication system between thecellular network and a mobile communication means. According to theexample of FIG. 5, the method comprises steps of setting up 200 of atleast two signalling radio bearers for transmission of signallingtraffic, and configuring 201 of how the signalling of higher layerprotocols is mapped to said signalling radio bearers.

According to an advantageous embodiment of the invention, the methodfurther comprises the step of routing 210 of signalling traffic dataunits via said at least two signalling radio bearers according topredefined rules.

In a further advantageous embodiment of the invention, said predefinedrules are set by a network element of a radio access network of thecellular telecommunication system.

In a still further advantageous embodiment of the invention, saidpredefined rules are set by a radio network controller.

According to an advantageous embodiment of the invention, in said stepof routing 210, signalling from different core network domains is routed210a via separate signalling radio bearers.

According to a further advantageous embodiment of the invention, in saidstep of routing 210, signalling of a higher layer protocol is routed210b via a signalling radio bearer specific to said higher layerprotocol.

According to a still further advantageous embodiment of the invention,in said step of routing 210, signalling traffic of a predefined group ofhigher layer protocols is routed 210c via a signalling radio bearercorresponding to said pre-defined group.

According to a still further advantageous embodiment of the invention,in said step of routing, signalling traffic of higher layer protocols isrouted via a signalling radio bearer based on a Quality of Serviceparameter attached to the higher layer protocol data.

In a further advantageous embodiment of the invention, said setting upand configuration of said signalling radio bearers is performed duringthe RRC connection establishment procedure.

In an even further advantageous embodiment of the invention, the methodcomprises steps of setting up of a further signalling radio bearerduring the RRC connection, and configuring the mapping of higher layersignalling to said further signalling radio bearer and previouslyexisting signalling radio bearers.

In an even further advantageous embodiment of the invention, the methodcomprises the step of reconfiguring the mapping of higher layersignalling to said signalling radio bearers.

In an even further advantageous embodiment of the invention, the methodcomprises the step of releasing a signalling radio bearer.

D. A Fourth Group of Advantageous Embodiments of the Invention

FIG. 6 illustrates the functional structure of a typical radio networkcontroller 400 of a cellular telecommunications network using as anexample the structure of a RNC of a UMTS radio network utilizing WCDMA(wideband code division multiple access) transmission method. Theinvention is not limited to the UMTS system, but can be used in othersimilar systems as well.

The radio network controller 400 comprises a switching fabric unit (SFU)450 to which several control processor units can be connected.Multiplexing units (MXU) 440 can be used between a number of processorunits and the SFU to map the low bit rate data flows from the processorunits into the high bit rate data flows of the SFU input ports. Thenetwork interface units (NIU) 410 handle the physical layer connectionsto different interfaces, such as Iub interface toward Node B elements,Iur interface towards other RNCs, and the Iu interface towards corenetwork nodes. The operations and maintenance unit (OMU) 430 containsthe RNC configuration and fault information and can be accessed fromexternal operations and maintenance center. The signalling units (SU)420 implement all the control and user plane protocols required in theRNC. Accordingly, the invention can be implemented in a RNC in thesignalling units 420. The invention can be implemented using means 460comprising software executed in the processors of the signalling units,which software causes the signalling units to perform according to theinvention.

In an advantageous embodiment of the invention, a network element of aradio access network of a cellular telecommunication system is provided.According to the embodiment, the network element is arranged to set upat least two signalling radio bearers for transmission of signallingtraffic and to configure how the signalling of higher layer protocols ismapped to said signalling radio bearers.

In a further advantageous embodiment of the invention, the networkelement is a radio network controller.

FIG. 7 illustrates roughly the functional structure of a typical mobilecommunication means (UE) 500. The UE comprises a user interface (UI)550, a control unit 540, a DSP unit 530, an RF unit 520, and an antenna510. The RF unit handles the radio frequency processing of received andtransmitted signals and converts the received signals to digital form.The DSP unit handles physical layer processing such as interleaving,channel coding, multiplexing, and segmentation. The DSP unit 530 canalso implement a part of or all of layer 2 radio protocols such as theMAC, RLC, and PDCP protocols. Layer 3 protocols such as the RRC, MM, andCM protocols and typically also a part of layer 2 protocols areimplemented in the control unit 540. Accordingly, the invention can beimplemented in a UE in the control unit 540. The invention can beimplemented using means 560 comprising software executed in theprocessor 570of the control unit, which software causes the control unitto perform according to the invention.

According to a further advantageous embodiment of the invention, amobile communication means for a cellular telecommunication system isprovided. According to the embodiment, the mobile communication means isarranged to route radio resource control protocol messages to at leasttwo signalling radio bearers as instructed by the cellulartelecommunication system.

E. Further Considerations

The present invention has several advantages. For example, the inventivesolution retains the beneficial aspects of the prior art solutionsdescribed previously, while retaining the present specifications asunmodified as possible. Further, the inventive approach allows keepingof integrity protection in one protocol layer only, i.e. in RRC. Theinventive method avoids the prior art problem of increasing thecomplexity of the PDCP protocol.

The inventive method is at the time of writing this patent applicationfully compatible with the present solutions regarding CND domainconcepts and routing of higher layer signalling messages from or to CNdomains based on CN domain identification information. The inventivemethod also requires no changes to Iu interface specifications. Theinventive method also allows prioritization between different types ofsignalling, such as between RRC signalling and higher layer signalling.The inventive method further allows the use of different QoS parametersfor different types of signalling. Further, the inventive solution willalso allow usage of different integrity algorithm for NAS (networkaccess stratum) and AS (access stratum) signalling, if that would belater required. This can be effected by allocating separate bearers forthese signalling flows, and applying a bearer specific integrityalgorithm for the bearers.

In the present application the term signalling is intended to covertransmission of messages of various protocols controlling variousaspects of the functioning of the cellular telecommunication systems,i.e. other transmissions than payload data transmissions.

The term higher layer protocol is in this application and particularlyin the accompanying claims intended to cover the Radio Resource Controlprotocol and any other layer 3 protocol acting between the mobilestation and the radio access network and all layer 3 or higher layersignalling protocols between the mobile station and core network, suchas for example the Mobility Management, Call Control, and SessionManagement protocols.

The invention is applicable in so called third generation mobilecellular systems, such as the UMTS system (universal mobiletelecommunication system) and corresponding systems. The various messagenames such as the RRC DIRECT TRANSFER message name are intended to beexamples only, and the invention is not limited to using the messagenames recited in this specification.

In view of the foregoing description it will be evident to a personskilled in the art that various modifications may be made within thescope of the invention. While a preferred embodiment of the inventionhas been described in detail, it should be apparent that manymodifications and variations thereto are possible, all of which fallwithin the true spirit and scope of the invention.

1. A method for transmitting signalling data between a cellular networkand a mobile communication means in a cellular telecommunication system,comprising the steps of: setting up at least two signalling radiobearers for transmission of signalling traffic, and configuring, throughaction of the cellular network, how the signalling of certain higherlayer protocols is mapped to said at least two signalling radio bearers.2. A method according to claim 1, additionally comprising the step ofrouting signalling traffic data units via said at least two signallingradio bearers according to predefined rules.
 3. A method according toclaim 2, wherein said predefined rules are set by a network element of aradio access network of the cellular telecommunication system.
 4. Amethod according to claim 3, wherein said predefined rules are set by aradio network controller.
 5. A method according to claim 2, wherein saidstep of routing signalling traffic data units via said at least twosignalling radio bearers comprises the substep of routing signallingrelated to different core network domains via separate signalling radiobearers.
 6. A method according to claim 2, wherein said step of routingsignalling traffic data units via said at least two signalling radiobearers comprises the substep of routing signalling of a higher layerprotocol via a signalling radio bearer specific to said higher layerprotocol.
 7. A method according to claim 2, wherein said step of routingsignalling traffic data units via said at least two signalling radiobearers comprises the substep of routing signalling traffic of apredefined group of higher layer protocols via a signalling radio bearercorresponding to said predefined group.
 8. A method according to claim2, wherein said step of routing signalling traffic data units via saidat least two signalling radio bearers comprises the substep of routingsignalling traffic of higher layer protocols via a signalling radiobearer based on a Quality of Service parameter attached to the higherlayer protocol data.
 9. A method according to claim 1, wherein the stepsof setting up and configuring said signalling radio bearers areperformed during a radio resource control (RRC) connection establishmentprocedure.
 10. A method according to claim 1, additionally comprisingthe steps of: setting up a further signalling radio bearer during aradio resource control (RRC) connection, and configuring the mapping ofhigher layer signalling to said further signalling radio bearer andpreviously existing signalling radio bearers.
 11. A method according toclaim 1, additionally comprising the step of later reconfiguring themapping of higher layer signalling to said signalling radio bearers. 12.A method according to claim 1, additionally comprising the step ofreleasing a signalling radio bearer.
 13. A network element of a radioaccess network of a cellular telecommunication system, wherein theimprovement lies in that the network element is arranged to set up atleast two signalling radio bearers for transmission of signallingtraffic and to configure how the signalling of higher layer protocols ismapped to said signalling radio bearers.
 14. A network element accordingto claim 13, wherein the network element is a radio network controller.15. A mobile communication means for a cellular telecommunicationsystem, wherein the improvement lies in that the mobile communicationmeans is arranged to route radio resource control protocol messages toat least two signalling radio bearers as instructed by the cellulartelecommunication system.
 16. An apparatus comprising: a control unit;and a processor in the control unit, the processor configured to causethe control unit to route one or more radio resource control (RRC) orhigher layer messages to at least two signaling radio bearers asinstructed by a cellular telecommunication system.
 17. The apparatus ofclaim 16, wherein the processor is further configured to cause thecontrol unit to determine a quality of service associated with at leastone of the one or more RRC or higher layer messages.
 18. The apparatusof claim 16, wherein the processor is further configured to cause thecontrol unit to route at least one of the one or more RRC or higherlayer messages to a signaling radio bearer corresponding with a qualityof service associated with the at least one RRC or higher layer message.19. The apparatus of claim 18, wherein the processor is furtherconfigured to cause the control unit to determine to which of apredefined set of quality of service classes the at least one RRC orhigher layer message has been assigned.
 20. The apparatus of claim 19,wherein separate signaling radio bearers exist for each quality ofservice class of the set of quality service classes, wherein the routingof one or more RRC or higher layer messages as instructed by a cellulartelecommunication system further comprises routing respective messagesto a signaling radio bearer associated with the quality of service classto which the message has been assigned.
 21. The apparatus of claim 16,wherein respective RRC or higher layer messages are associated with acore network domain, and wherein the processor is further configured tocause the control unit to route respective RRC or higher layer messagesbased at least in part on the core network domain with which therespective messages are associated.
 22. The apparatus of claim 21,wherein the core network domain is a circuit switched core networkdomain or a packet switched core network domain, and wherein a separatesignaling radio bearer exists for each of the circuit switched corenetwork domain and the packet switched core network domain.
 23. Theapparatus of claim 16, wherein the processor is further configured tocause the control unit to route respective RRC or higher layer messagesto the at least two signaling radio bearers based at least in part onwhich of a plurality of protocols is associated with the respectivemessages.
 24. The apparatus of claim 23, wherein a separate signalingradio bearer exists for each of the plurality of protocols.
 25. Theapparatus of claim 16, wherein the processor is further configured tocause the control unit to route the one or more RRC or higher layermessages as instructed by a network element of a radio access network ofthe cellular telecommunication system.
 26. The apparatus of claim 25,wherein the network element comprises a radio network controller. 27.The apparatus of claim 16, wherein the processor is further configuredto cause the control unit to receive a RRC connection setup messagecomprising an indication of a number of signaling radio bearers to beestablished, an indication of one or more radio link control parametersneeded for each of the signaling radio bearers to be established, and anindication of which RRC or higher layer messages are mapped to each ofthe signaling radio bearers to be established.
 28. The apparatus ofclaim 16, wherein the processor is further configured to cause thecontrol unit to receive a radio bearer setup message associated with asignaling radio bearer to be established, the radio bearer setup messagecomprising instructions for routing at least one of the RRC or higherlayer messages to the associated signaling radio bearer.
 29. Theapparatus of claim 16, wherein the one or more RRC or higher layermessages are selected from a mobility manager layer message, aconnection management layer message, a session management layer message,or a packet switched domain mobility management layer message.
 30. Anapparatus comprising: a control unit; and a processor in the controlunit, the processor configured to cause the control unit to route one ormore radio resource control (RRC) protocol messages to at least twosignaling radio bearers as instructed by a cellular telecommunicationssystem.
 31. The apparatus of claim 30, wherein the one or more RRCprotocol messages comprise one or more messages generated by a RRC layerand one or more messages generated by at least one layer higher than theRRC layer.
 32. The apparatus of claim 31, wherein the one or moremessages generated by the at least one layer higher than the RRC layerare selected from a mobility management layer message, a connectionmanagement layer message, a session management layer message, or apacket switched domain mobility management layer message.
 33. Theapparatus of claim 31, wherein at least one of the at least twosignaling radio bearers is associated with the one or more RRC protocolmessages generated by the RRC layer.
 34. The apparatus of claim 31,wherein at least one of the at least two signaling radio bearers isassociated with the one or more RRC protocol messages generated by theat least one layer higher than the RRC layer.
 35. An apparatuscomprising: a control unit; and a processor in the control unit, theprocessor configured to cause the control unit to route one or morehigher layer protocol messages to at least three signaling radio bearersas instructed by a cellular telecommunication system.
 36. The apparatusof claim 35, wherein at least one of the one or more higher layerprotocol messages comprises a message generated by a radio resourcecontrol (RRC) protocol layer.
 37. The apparatus of claim 36, wherein atleast two of the at least three signaling radio bearers are associatedwith the RRC protocol layer message.
 38. The apparatus of claim 37,wherein one of the signaling radio bearers associated with the RRCprotocol layer message is configured for unacknowledged mode transfer ofthe RRC protocol layer message.
 39. The apparatus of claim 37, whereinone of the signaling radio bearers associated with the RRC protocollayer message is configured for acknowledged mode transfer of the RRCprotocol layer message.
 40. The apparatus of claim 36, wherein at leastone of the one or more higher layer protocol messages comprises amessage generated by a protocol layer higher than the RRC protocollayer.
 41. The apparatus of claim 40, wherein at least one of the atleast three signaling radio bearers is associated with the messagegenerated by a protocol layer higher than the RRC protocol layer.
 42. Anetwork element of a radio access network of a cellulartelecommunication system, wherein the improvement lies in that thenetwork element comprises: means for setting up at least two signalingradio bearers for transmission of signaling traffic and means forconfiguring how the signaling of higher layer protocols is mapped to thesignaling radio bearers.
 43. A mobile communication means for a cellulartelecommunication system, wherein the improvement lies in that themobile communication means comprises: means for routing radio resourcecontrol protocol messages to at least two signaling radio bearers asinstructed by the cellular telecommunication system.
 44. An apparatuscomprising: a mobile communications device; and a control unit in themobile communications device configured to route messages to at leasttwo signaling radio bearers as instructed by a cellulartelecommunication system.
 45. The apparatus of claim 44 wherein themessages comprise one or more radio resource control and higher layerprotocol messages.
 46. The apparatus of claim 45, wherein the messagesare routed according to predefined rules.
 47. The apparatus of claim 46,wherein the predefined rules are set by a network element of a radioaccess network of the cellular telecommunication system.
 48. Theapparatus of claim 44, wherein the control unit is further configured toroute messages of a higher layer protocol to a signaling radio bearerspecific to the higher layer protocol.
 49. The apparatus of claim 44,wherein the control unit is further configured to route messages of apredefined group of higher layer protocols to a signaling radio bearercorresponding to the predefined group.
 50. The apparatus of claim 44,wherein the control unit is further configured to route messages ofhigher layer protocols to a signaling radio bearer based on a Quality ofService parameter attached to the higher layer protocol data.
 51. Theapparatus of claim 50, wherein the control unit is further configured tocheck at least one Quality of Service class, wherein a separate radiobearer is set up for each of the at least one Quality of Service class.52. A method comprising: in a user equipment, routing one or more radioresource control protocol messages to at least two signaling radiobearers as instructed by a network.
 53. The method of claim 52, whereinthe one or more radio resource control protocol messages comprise higherlayer protocol data, such that routing the one or more radio resourcecontrol protocol messages comprises routing higher layer protocol datato the at least two signaling radio bearers as instructed by thenetwork.
 54. The method of claim 53, further comprising routing thehigher layer protocol data based on a Quality of Service parameterattached to the higher layer protocol data.
 55. The method of claim 52,further comprising routing the one or more radio resource controlprotocol messages based on a Quality of Service parameter attached tothe radio resource control protocol message.